size of a battery used in portable devices such as radios, music players, flashlights...usually a 1.5V (volt)in Alkaline or a 1.2V in rechargeable. Can be used alone, or in combination with other AA batteries as decided by the device manufacturer.

zeke:get a package of AA batteries for me at the store
zack: ya want 48 from Costco or 2 from 7-11??